1. Field of the Invention
This invention relates to a probe for an optical near field microscope, said probe comprising a planar carrier carrying a probe tip at least partially consisting of a transparent material. The invention also relates to a method for producing such probe.
2. Background Art
Optical near field microscopes exploit the effect that a high optical resolution can be realized with the aid of a probe with a very small aperture at a very short distance to a sample surface. In order to achieve this, probes are for example produced from optical waveguides, which run to a point at an end due to drawing at high temperatures. The end of the fibre is coated with metal so that a small aperture arises at the pointed end of the optical waveguide, through which light can emanate. When using the microscope, the tip is brought to a very small distance to a sample surface, whereby the surface is illuminated by the small aperture of the fibre probe and the fibre probe is scanned over the sample surface at a very short distance to it.
In this respect the spatial resolution of the image acquired from the sample is essentially dependent on the tip radius of the fibre, the size of the aperture and the accuracy of guiding the fibre in the vertical direction when scanning over the sample.
By means of a piezo-mechanical drive or a shear-force mechanism, it is already possible to achieve very accurate guiding of the fibre probe in the vertical direction during scanning. However, the optical waveguide probes could only previously be manufactured with an aperture size of about 100 nanometers, which is an improvement of the optical resolution of an optical near field microscope compared to a conventional light microscope, but does not increase it by orders of magnitude.
In addition, the dimensions of the drawn fibres cannot be reproduced to the desired extent, so that after changing the fibre tip, the images from the optical near field microscope can vary with regard to resolution and contrast. Furthermore, only one single tip can be produced in each case with the fibre drawing method, so that the probes can be produced only with low productivity and therefore high costs.
DE 199 26 601 A1 describes a generic probe and an associated method in which the probe exhibits a funnel-shaped probe tip which has an internal cavity, the said probe tip extending through the thickness of a bending beam. Here, the internal side edges of the cavity funnel structure are covered with an oxide layer. For the manufacture of this probe a structure with a funnel-shaped pit and a retaining element are produced in separate process sequences. These two structures are then joined together in order to form the probe tip from the combination by etching.
Owing to the large number of process steps, this technology is complicated and expensive. In addition, inaccuracies in the probe dimensions can arise due to the joining step of the individual structures. With this structure it is not possible to pass light by means of the probe directly to the tip of the probe. It is only possible to position a light beam above the funnel opening so that light can impinge on the sample through the tip region of the probe tip.
U.S. Pat. Nos. 6,333,497 and 6,211,532 describe the probes and associated methods for optical near field microscopes with which evanescent waves are detected by the probe. With these microscopes the sample is illuminated from the rear and the probe detects the evanescent radiation and converts it into a photoelectric current, the signal of which is evaluated for generating an image. In the methods shown a hollow funnel-shaped pit is in each case etched in a first substrate and the internal surface of the pit is coated with a transparent material. The first substrate is then joined to a second substrate, whereupon the first substrate is etched so far until an internal hollow probe tip is formed from the second substrate. The second substrate is thinned down in a region below the probe tip such that a thin carrier is created on which the probe tip is placed.
These methods exhibit a large number of process steps, whereby in particular the joining step between the individual substrates is critical with respect to the achieved reproducibility of the probe dimensions. Due to the evanescent functioning principle, with these types of probe there is also no possibility provided for passing light to the respective probe tip.